Implementing a Night Sky with stars, the moon?
One possible solution is to use HDRIs like the ones available for free at HDRI haven.

They have night skies.

Use is trivial (see below). Also they "rotate" realistically with the camera, which is harder to achieve otherwise.

Go to your World settings, click on the dot at the right of Color, choose Environment, then pick the HDRI file you downloaded. You can adjust the strength afterwards.

Assuming 2.80 (works with 2.79 though).